[modules] Fix bugs in assignments to exported variables.

test/mjsunit/modules-skip-init3.js

Index: test/mjsunit/modules-skip-init3.js
diff --git a/test/mjsunit/modules-skip-init3.js b/test/mjsunit/modules-skip-init3.js
index eac1ae172b1950c9d632ab6e15199afc273fa49a..589b2cfb16c588f295b050af1214fa987bfbf86f 100644
--- a/test/mjsunit/modules-skip-init3.js
+++ b/test/mjsunit/modules-skip-init3.js
@@ -10,6 +10,12 @@ assertThrows(() => x, ReferenceError);
 assertThrows(() => y, ReferenceError);
 assertThrows(() => z, ReferenceError);
 
+assertThrows(() => v = 666, TypeError);
+assertThrows(() => w = 666, TypeError);
+assertThrows(() => x = 666, TypeError);
+assertThrows(() => y = 666, TypeError);
+assertThrows(() => z = 666, TypeError);
+
 export function check() {
   assertEquals({value: 40, done: true}, v().next());
   assertEquals(41, w);